A high-pressure pump has a plunger which reciprocates to pressurize fuel in a pressurization chamber. The pressurized fuel is discharged from the pressurization chamber. Japanese patent No. 4530053 (US-2009/0185922A1) discloses a high-pressure pump which has a pulsation damper in a fuel chamber. The pulsation damper is comprised of two diaphragms. The diaphragms are deformed according to a pressure of the fuel in the fuel chamber, so that a pressure pulsation of low-pressure fuel in a fuel supply system is reduced. The fuel supply system includes the fuel chamber and a fuel supply pipe communicating with the fuel chamber.
When a frequency of the pressure pulsation of the low-pressure fuel agrees with a characteristic frequency of the diaphragms, vibration amplitude of the diaphragms becomes large. That is, a resonance occurs. The resonance deteriorates a pulsation-reduction function of the pulsation damper. In the above high-pressure pump, a characteristic frequency of one diaphragm is made different from a characteristic frequency of another diaphragm in order to avoid that both diaphragms resonate simultaneously.
However, the resonance of the diaphragms itself can not be restricted. Therefore, when one of the diaphragms resonates, the pressure pulsation of the fuel in the fuel chamber cannot be reduced. The pressure pulsation may generate a noise in the fuel supply passage.
Moreover, since the plunger of the high-pressure pump is driven by a crankshaft of an engine, the pressure pulsation frequency of the low-pressure fuel depends on an engine speed. Therefore, the frequency of the pressure pulsation at which the resonance occurs varies according to an engine specification and specifications of the fuel supply pipes of the high-pressure pump. The characteristic frequency of each diaphragm is required to be adjusted according to a vehicle to which the high-pressure pump is provided.